1. Field of the Invention
The present invention relates to an electronic component element and a composite module including the same, and particularly relates to, for example, a surface acoustic wave filter and a front-end module including the same.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2008-227748 describes a surface acoustic wave (SAW) filter (hereinafter, referred to as SAW filter) in which a principal surface side of a piezoelectric substrate having a comb-shaped electrode (IDT: Interdigital Transducer) formed thereon is a mounted surface to a board. In the SAW filter, a resin sealing layer made of a resin is provided on an upper surface of the comb-shaped electrode, and a through (via-hole) electrode is formed so as to extend through the resin sealing layer for connecting the comb-shaped electrode to a bump electrode formed on the surface of the resin sealing layer. For a composite module including the SAW filter described in Japanese Unexamined Patent Application Publication No. 2008-227748, there is particularly a strong demand for height reduction, and the SAW filter also has a feature that its thickness can be decreased by the thickness of a package substrate required in the related art, since it has the structure as described in Japanese Unexamined Patent Application Publication No. 2008-227748.
However, in the SAW filter described in Japanese Unexamined Patent Application Publication No. 2008-227748, since the resin sealing layer having a different coefficient of linear expansion from that of the piezoelectric substrate is formed near the piezoelectric substrate, the resin contracts in heating and curing the resin sealing layer. When the resin contracts, compressive stress generated at the time of the contraction is applied to the piezoelectric substrate via the through electrode and the board may be deformed. When the piezoelectric substrate is deformed, the interval of the comb-shaped electrode on the piezoelectric substrate or the like is changed and thus there is the problem that the characteristics of the SAW filter are changed.